Solar panel comprising a structure, at least two photovoltaic cells and a barrier

ABSTRACT

This solar panel ( 12 ) includes a structure ( 14 ) and at least two photovoltaic cells ( 16 A,  16 B) each defining a lateral contact face ( 30 A,  30 B) and including a base element ( 20 A,  20 B), a grid of electric conductors ( 24 A,  24 B) and a protective element ( 22 A,  22 B) made from transparent material, the grid ( 24 A,  24 B) including at least one conductive wire extending along the lateral contact face ( 30 A,  30 B). 
     The cells ( 16 A,  16 B) are arranged on the structure ( 14 ) such that at least part of each of the lateral contact faces ( 30 A,  30 B) is arranged across from the other part. The solar panel ( 12 ) further includes a barrier ( 18 A) made from dielectric material arranged on the structure ( 14 ) between the lateral contact faces and extending along the opposite parts of these faces ( 30 A,  30 B).

FIELD OF THE INVENTION

The present invention relates to a solar panel in particular including astructure and at least two photovoltaic cells.

The invention is in particular applicable in the aerospace domain. Thus,the solar panel according to the invention is on board a spacecraft suchas a satellite, for example, and is an electrical power source for sucha vehicle.

BACKGROUND OF THE INVENTION

In general, the satellite includes one or several solar panels, alsocalled solar generators, which are used to power at least someelectrical components of the satellite.

The modern structures of satellites are based on the “all electrical”concept, consisting of using propulsion of the on-board electricalpropellant type. There is then a need to increase the capacities ofsolar generators to produce electrical energy.

In this context, solar generators must provide voltages of up to severalhundred volts (typically 350 V for the current propellants, or even 600V for some motors being studied).

It is also known that the electrical components of satellites, and inparticular electrical current conductors used in these components, areparticularly exposed to short circuit or breaking risks (open circuit)if an electric arc appears.

Indeed, in an aerospace environment with no atmosphere, a precursorphenomenon of the electrostatic discharge, micrometeorite impact,high-voltage, etc. type may generate local plasma. The latter, byexpanding, makes the environment conductive and may establish a shortcircuit between differentially polarized parts. Such a short circuit isalso known as an electric arc.

The problem of the establishment of electric arcs becomes particularlyrelevant in light of solar generators due to the available photovoltaicpower.

In particular, means for preventing the establishment of electric arcsused in the current structures are no longer sufficient to perform thisrole effectively. This is in particular due to the required increase inthe voltage of the electric current provided by these generators.

Thus, it has been noted that when the electric voltage generated bythese solar generators become significant, electric arcs appeartemporarily, quasi-permanently or permanently between differentconductors of these generators.

One can then see that these arcs can greatly damage the solar panels andcause losses of the available photovoltaic power partially (damage of acell, a row or an entire section), damage of an entire panel or theentire wing of the solar generator).

SUMMARY OF THE INVENTION

The present invention aims to propose a solar panel in which the risk ofestablishment of an electric arc is greatly decreased.

To that end, the invention relates to a solar panel including astructure; at least two photovoltaic cells, each cell defining a lateralcontact face and including a base element, a grid of electric conductorsand a protective element made from transparent material, the grid beingarranged between the protective element and the base element andincluding at least one conductive wire extending along the lateralcontact face of the cell; the two cells being arranged on the structuresuch that at least part of each of the lateral contact faces is arrangedacross from the other part and such that the protective elements ofthese cells form a panel surface; the solar panel being characterized inthat it further includes a barrier made from a dielectric materialarranged on the structure between the lateral contact faces of the twophotovoltaic cells, extending along the opposite parts of these facesand protruding relative to the panel surface.

According to other advantageous aspects of the invention, the panelcomprises one or more of the following features, considered alone oraccording to all technically possible combinations:

-   -   it is designed to operate in an environment in which the        direction perpendicular to the panel surface moves away from a        lighting direction by a maximum separation angle smaller than        90°, the lighting direction being defined by a straight line        passing through the center of a lighting source and a        predetermined point of the panel; and in that the barrier and/or        the cells are arranged such that the shade generated by the        barrier when the direction perpendicular to the panel surface        moves away from the lighting direction by the maximal separation        angle is substantially outside each of the two cells;    -   it is on-board a spacecraft;    -   the cross-section of the barrier forms an isosceles triangle,        the base of which is adjacent to the structure, the angle        opposite the base being twice the maximum separation angle;    -   the structure has an elongated shape along a longitudinal axis        perpendicular to the transverse axis; and the grid of each cell        includes a plurality of conductive wires extending along the        longitudinal axis;    -   the grid of each cell assumes the form of a comb, the teeth of        which are formed by conductive wires extending along the        longitudinal axis;    -   it is on board a spacecraft rotating around an orbit; and the        longitudinal axis is perpendicular to the plane comprising the        orbit;    -   the barrier is made from a flexible material, the barrier being        suitable for being folded in the space delimited by the two        lateral contact faces without protruding relative to the panel        surface;    -   the barrier is made from a polyimide polymer;    -   the barrier is a concentrator; and    -   the barrier is arranged between each pair of photovoltaic cells        between which the voltage is greater than 30 V.

BRIEF DESCRIPTION OF THE DRAWINGS

These features and advantages of the invention will appear upon readingthe following description, provided solely as a non-limiting example,and done in reference to the appended drawings, in which:

FIG. 1 is a schematic view of a geostationary satellite in particularincluding a solar panel according to a first embodiment of theinvention;

FIG. 2 is a schematic top view of the solar panel of FIG. 1;

FIG. 3 is a schematic longitudinal sectional view of part of a solarpanel of FIG. 1 illustrating the first embodiment of the invention;

FIG. 4 is a view similar to that of FIG. 3 of a solar panel according toa second embodiment of the invention;

FIG. 5 is a view similar to that of FIG. 3 of a solar panel according toa third embodiment of the invention; and

FIG. 6 is a view similar to that of FIG. 2 of a solar panel according toa fourth embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In the description, when the term “about” is used in relation with anumerical value, it must be understood that the given numerical value isapproximate with a margin of error that is determined by one skilled inthe art in each considered case. As an example, this margin of error isequal to +10% or −10% of the given value.

In FIG. 1, the geostationary satellite 10 includes two solar panels 12and 12′ according to the invention arranged on either side of a body 13of the satellite 10 in a manner known in itself.

The satellite 10 rotates around the Earth T following an orbit O₁. TheEarth then rotates around the Sun following an orbit O₂. The line Epassing through the center of the Sun S and a fixed point of the panel12 and oriented toward the satellite 10 will be denoted hereinafterusing the term “lighting direction E”.

The solar panels 12, 12′ are able to produce an electric currentdelivering the power of several kilowatts. The voltage of this currentfor example extends from 28 V to 160 V, or up to 350 V or more.

The solar panels 12, 12′ are substantially identical to one another.Thus, hereinafter, only the solar panel 12 will be explained in detailin particular in reference to FIGS. 2 and 3.

As illustrated in FIG. 2, the solar panel 12 for example has an elongateshape along a longitudinal axis Y perpendicular to a transverse axis X.This shape is for example substantially rectangular. In this case, thelongitudinal axis Y extends along the length of the rectangle and thetransverse axis X extends along the width of this rectangle.

The satellite 10 rotates around the Earth T while following the orbitO₁, for example such that the longitudinal axis Y is perpendicular tothe plane comprising this orbit O₁. In this case, the longitudinal axisY is called North-South axis.

The solar panel 12 comprises a structure 14, a plurality of photovoltaiccells 16A to 16N able to generate an electric current and arranged onthe structure 14 while forming rows along the transverse axis X, and aplurality of dielectric barriers 18A to 18N arranged between the rows ofcells 16A to 16N and extending along the transverse axis X, as will beexplained hereinafter. Furthermore, the first and last cells of each roware called end cells hereinafter.

The structure 14 is suitable for being fastened to the body 13 of thesatellite 10 and has the cabling means necessary to conduct anelectrical current between the cells 16A to 16N and toward the body 13of the satellite 10.

Each cell 16A to 16N is for example able to produce an electricalcurrent of about 0.5 A, or 0.8 A, or even 1.6 A based on the unit sizeof the solar cells, even larger.

In the example of FIG. 2, the cells 16A to 16N are arranged on thestructure 14 in nine rows, each row being made up of six cells andextending along the transverse axis X. In FIG. 2, only the first cells16A and 16B of the first two rows, the last cell 16N of the last row,the barriers 18A, 18B separating the first three rows from one anotherand the barrier 18N separating the last row from the next to last row,bear references.

The cells 16A to 16N form a panel surface 19 visible in FIG. 3.

The panel surface 19 defines a direction P perpendicular to thissurface. The perpendicular direction P moves away from the lightingdirection E along a separation angle α. During different phases of therotation of the satellite 10, the separation angle α varies from 0° upto the value of a maximum separation angle α_(max).

The maximum separation angle α_(max) is for example equal to about23.45°. Such a value of the separation angle is intended to preventshadows cast on the panel surface 19.

The cells 16A to 16N are substantially identical to one another.Furthermore, the barriers 18A to 18N separating the rows of cells arealso substantially identical to one another.

In particular, seen from above (the view of FIG. 2), each cell 16A to16N has a hexagonal shape with two right angles adjacent to a same side,called long side, and four other angles greater than 90°, two of theseangles being adjacent to a side parallel to the long side, called shortside. The shape is symmetrical relative to an axis perpendicular to theshort side and the long side.

In other words, seen from above, each cell 16A to 16N assumes the formof a rectangle with two symmetrically canted angles.

In a same row, the cells 16A to 16N are arranged traditionally, i.e.,such that their long side (or the short side) is perpendicular to thetransverse axis X.

Furthermore, in a same row, the cells 16A to 16N are connected to oneanother by the cabling means extending parallel to the transverse axis Xand traditionally called inter-connectors (not shown in FIG. 2).

Lastly, as is known in itself, between adjacent cells of a same row, thevoltage is not very different and is for example comprised between 0.5 Vand 2.5 V depending on the technology of the cells.

Between each pair of different rows, the cabling means connect only twoadjacent cells, for example the end cells located on the same side ofthe panel 12.

Thus, in the example of FIG. 2, the cabling means connect the cells of asame row transversely and the cells of different rows longitudinally.

As an example, in FIG. 2, the last cells of the first two rows areconnected by the same cabling means. Like in the previous case, thevoltage between these adjacent cells is for example comprised between0.5 V and 2.5 V based on the technology of the cells.

In the example embodiment of FIG. 2, each barrier 18A to 18N extendsalong the transverse axis X substantially between the end cells of asame row, i.e., along the entire corresponding row. In this case, thecabling means between different rows pass by bypassing the correspondingbarrier or below the panel as is done traditionally for each cell row.

However, in the general case, the expense of each barrier 18A to 18Nalong the corresponding row can be adjusted based on the arrangement ofthe cells 16A to 16N and the cabling means.

In particular, when the end cells of two adjacent rows are connected bythe cabling means, it is not necessary to extend the correspondingbarrier 18A to 18N up to these cells given that the voltage betweenthese cells is relatively low (between 0.5 V and 2.5 V).

In general, according to the invention, a barrier 18A to 18N is arrangedbetween each pair of cells 16A to 16N between which the voltage isgreater than 30 V.

Particular attention will be given to the locations where, depending onthe embodiment, one could have a row end with a high voltage near a loopon a same cell row. The barrier should then protect the cells having ahigh voltage with a sufficient distance between the cells both at aheight and flush. The cabling of the adjacent row should then bypass ortraverse the barrier. The barrier may have a notch to be able to beplaced after the cabling.

Lastly, when the cells 16A to 16N have more complex shapes (trapezoidal,half-hexagonal or half-octagonal, or the like), the barriers 18A to 18Nare no longer straight, but forms zigzags. In this case, the cells 16 to16N are oriented such that the corresponding barriers 18A to 18Ngenerate the least possible amount of shadow over its greatest possiblelength.

Subsequently, only the adjacent cells 16A and 16B and the barrier 18Aseparating these cells 16A, 16B will be explained in more detail inparticular in reference to FIG. 3, illustrating part of the solar panel10 in cross-section.

As illustrated in FIG. 3, each of the cells 16A, 16B includes a baseelement 20A, 20B fixed on the structure 14, a protective element 22A,22B covering the base element 20A, 20B, and a grid of electricalconductors 24A, 24B arranged between the base element 20A, 20B and theprotective element 22A, 22B.

The base element 20A, 20B is known in itself. Such an element inparticular comprises a conductive plate, a lower layer made up of aP-type semiconductor and covering the conductive plate, and an upperlayer made up of a N-type semiconductor and covering the lower layer.

The protective element 22A, 22B is made from a transparent material suchas glass, and for example, it makes it possible to protect the cell 16A,16B from the radiative dose while allowing the light to pass toward thebase element 20A, 20B. This element 22A, 22B is also known as“coverglass”.

The grid 24A, 24B includes a plurality of conductive wires arrangedhomogeneously over the entire surface of the base element 20A.

In particular, the grid 24A, 24B assumes the form of a comb (visible inFIG. 2) with the conductive wires extending along the transverse axis X.In a manner known in itself, such a structure allows the light to passtoward the base element 20A, 20B.

Each of the two cells 16A, 16B defines a lateral contact face 30A, 30B.The lateral contact faces 30A, 30B are arranged across from one another.Thus, a conductive wire of each of the grids 24A, 24B runs alongside thecorresponding lateral contact face 30A, 30B.

The lateral contact faces 30A, 30B are separated from one another by adistance d.

The barrier 18A is arranged between the lateral contact faces 30A, 30Bsymmetrically.

The barrier 18A protrudes relative to the panel surface 19. In FIG. 3,reference h corresponds to the length of the protruding part extendingin the perpendicular direction P, from the barrier 18A relative to thepanel surface 19, and reference δ corresponds to the thickness of theprotective elements 22A, 22B. Thus, the barrier 18A protrudes relativeto the ends of the grids 24A, 24B in contact with the protectiveelements 22A, 22B by a value h+δ.

The barrier 18A is a thin plate fastened on the structure 14 and forexample made from glass or from a polyimide polymer, in particular inthe form of the material known under the name Kapton® or UPILEX®.However, more generally, the barrier 18A can be made from any dielectricmaterial. Advantageously, it is possible to choose from dielectricswithstanding the temperature well (Polyimide Kapton™, Teflon™,Coverglass of all types, etc.)

Advantageously, the material of the barrier 18A is flexible. In thiscase, the barrier 18A is suitable for being folded in the spacedelimited between the two lateral contact faces 30A and 30B withoutprotruding relative to the panel surface 19. Such a configuration of thebarrier 18A for example makes it possible to keep it folded when thesatellite is launched and stationed, i.e., before deployment of thesolar panels 12, 12′.

According to the first embodiment of the invention, the cells 16A and16B are arranged such that the shade generated by the barrier 18A whenthe direction perpendicular P to the panel surface 19 moves away fromthe lighting direction E of the maximum separation angle α_(max), issubstantially outside each of the two cells 30A, 30B.

One can then see that the present invention has a certain number ofadvantages.

First, it has been demonstrated that when the shortest path betweenconductive components of the adjacent photovoltaic cells increases, therisk of establishment of an electric arc between these components isgreatly decreased.

Thus, a dielectric barrier inserted between two lateral contact faces ofcells and protruding from the panel surface makes it possible to extendthis path and thereby decrease the risk of establishment of an electricarc.

Furthermore, by choosing the dimensions of the protruding part of thisbarrier in a particular manner, it is possible to minimize the risk ofestablishment of an electric arc while retaining a compact arrangementof the cells on the structure.

According to the first embodiment of the invention, the adjacent cellsare separated from one another only so that the barrier does notgenerate shade cast on the working surface of the cells even when thelighting direction E and the perpendicular direction P form the maximalseparation angle α_(max). This then makes it possible to retain the sameproductivity of the panel according to the invention relative to aconventional panel, irrespective of the position of the satellite.

Lastly, the flexibility of the barriers ensures that the presence of thebarriers on the panels does not require any structural change of thesepanels. Indeed, the solar panels according to the invention can befolded on one another in particular during the launch phase of thesatellite, without the barriers hindering this folding.

A solar panel 112 according to a second embodiment of the invention isillustrated in FIG. 4.

The solar panel 112 is similar to the solar panel 12 previouslydescribed and in particular includes a structure 14 and photovoltaiccells 16A to 16N substantially identical to those previously described.

The solar panel 112 further includes a plurality of barriers 118A to118N that differ from the barriers 18A to 18N previously described onlyby their shape in cross-section.

Thus, as illustrated in FIG. 4 in connection with the barrier 118A, eachbarrier 118A to 118N has a cross-section in the shape of an isoscelestriangle.

The length of the base of this triangle is equal to the value of thedistance d previously mentioned, the triangle protruding relative to thepanel surface 19 by the same value h previously mentioned.

The angle β of the triangle across from the base is equal to about twomaximal separating angles α_(max).

Thus, like in the previous case, the barriers 118A to 118N make itpossible to minimize the risk of establishment of an electric arcbetween each adjacent pair of cells and do not generate shade cast onthese cells.

A solar panel 212 according to a third embodiment of the invention isillustrated in FIG. 5.

The solar panel 212 is similar to the solar panel 112 previouslydescribed and in particular includes a structure 14 and photovoltaiccells 16A to 16N substantially identical to those previously described.

The solar panel 212 further includes a plurality of barriers 218A to218N that differ from the barriers 118A to 118N previously described inthat each barrier 218A to 218N assumes the form of a concentrator.

Thus, as illustrated in FIG. 5 in connection with the barrier 218A, eachbarrier 218A to 218N has a cross-section in the shape of a curvedisosceles triangle with a straight base.

The length of the base of this triangle is equal to the value of thedistance d previously mentioned, the triangle protruding relative to thepanel surface 19 by the same value h previously mentioned.

The angle β of the triangle across from the base is equal to about twomaximal separating angles α_(max).

The surface of the barriers 218A to 218N exposed to the rays of the SunS is covered by a reflective material. The shape of the curved faces ofthe barriers 218A to 218N is suitable for reflecting the rays toward thecorresponding cells.

Like in the previous cases, the barriers 218A to 218N make it possibleto minimize the risk of establishment of an electric arc between eachadjacent pair of cells and do not generate shade cast on these cells.

Furthermore, according to this embodiment, the productivity of the solarpanel 213 is improved owing to the barriers 218A to 218N assuming theform of concentrators.

A solar panel 312 according to a fourth embodiment of the invention isillustrated in FIG. 6.

The solar panel 312 is similar to the solar panel 12 previouslydescribed and in particular includes a structure 14.

The solar panel 312 further includes a plurality of photovoltaic cells316A to 316N arranged on the structure 14 while forming rows along thelongitudinal axis Y and a plurality of barriers 318A to 318N arrangedbetween the rows of cells 316A to 316N. Like in the previous case, thefirst and last cells of each row are called end cells hereinafter.

The solar panel 312 differs from the panels previously described solelyby the arrangement of the cells 316A to 316N on the structure 14.

In particular, according to this embodiment, the cells 316A to 316N arearranged on the structure 14 in four rows, each row being made up of nomore than twelve cells and extending along the longitudinal axis Y. InFIG. 6, only the first cells 316A and 316B of the first rows and thelast cell 316N of the last row bear references.

Furthermore, according to this embodiment, in a same row, the cells 316Ato 316N are connected to one another by the cabling means extendingparallel to the longitudinal axis Y.

Like in the previous case, between adjacent cells of a same row, thevoltage is not very different and is for example comprised between 0.5 Vand 2.5 V depending on the technology of the cells.

Between each pair of different rows, the cabling means connect thecorresponding cells, and preferably end cells, while bypassing thecorresponding barrier 318A to 318N.

In the example of FIG. 6, the barriers 318A to 318N extend all along thecorresponding rows. However, like in the previous case, the expanse ofthe barriers 318A to 318N can be shortened in the locations where thecabling means connect two cells of the different rows in light of arelatively low voltage between these cells.

However, according to the invention, a barrier 318A to 318N is arrangedbetween each pair of cells 316A to 316N between which the voltage isgreater than 30 V.

Each barrier 318A to 318B is similar to one of the barriers 18A, 118A or218A previously described.

Like in the previous cases, each barrier 318A to 318N protrudes relativeto the panel surface 19 by the same value h previously mentioned, tominimize the risk of an electric arc being established.

The arrangement of the barriers 318A to 318N along the longitudinal axisY constitutes a particular advantage of the invention according to thefourth embodiment. Indeed, such an arrangement of the barriers 318A to318N relative to the Sun S causes the barriers 318A to 318N not togenerate shade cast on the cells.

Thus, the distance d between the lateral contact faces of each pair ofcells 316A to 316N belonging to the different rows can advantageously bereduced in order to make the arrangement of these cells on the structure14 more compact.

According to this embodiment, this distance d is for example equal to0.9+/−0.3 mm.

Furthermore, unlike the arrangement of these cells illustrated in FIG.2, there is no longer a need to separate the cells along thelongitudinal axis Y. Thus, the cells in FIG. 6 are arranged on thestructure 14 particularly compactly, in particular along thelongitudinal axis Y and without modifying the typical dimensions of asolar panel without barriers.

Of course, other embodiments of the invention are also possible.

In particular, it is possible to combine at least some of theembodiments previously described in order to obtain a solar panelincluding at least one barrier minimizing the risk of an electric arcbeing established between two adjacent cells without generating shadecast on these cells.

The barrier can be continuous or discontinuous when the voltage dropsagain below 30 V or to facilitate a folding mode when the gap betweencells is not straight due to the shape of the cells (for example,trapezoidal).

The dielectric barrier can be made from a shape memory material, toregain the desired shape after deployment or lighting (by energytransmission).

Furthermore, it must be understood that the solar panel according to theinvention can be on board any moving vehicle other than a satellite, orin general can be used independently of any moving vehicle, for examplein a stationary configuration on a land surface.

1. A solar panel, including: a structure; at least two photovoltaic cells, each cell defining a lateral contact face and including a base element, a grid of electric conductors and a protective element made from transparent material, the grid being arranged between the protective element and the base element and including at least one conductive wire extending along the lateral contact face of the cell; the two cells being arranged on the structure such that at least part of each of the lateral contact faces is arranged regarding the other part and such a way that the protective elements of these cells form a panel surface; wherein the solar panel further includes a barrier made from dielectric material arranged on the structure between the lateral contact faces of the two photovoltaic cells, extending along the opposite parts of these faces and protruding relative to the panel surface.
 2. The panel according to claim 1, designed to operate in an environment in which the direction perpendicular to the panel surface moves away from a lighting direction by a maximum separation angle smaller than 90°, the lighting direction being defined by a straight line passing through the center of a lighting source and a predetermined point of the panel; wherein the barrier and/or the cells are arranged such a way that the shade generated by the barrier when the direction perpendicular to the panel surface moves away from the lighting direction of the maximum separation angle, is substantially outside each of the two cells.
 3. The panel according to claim 1, being on board a spacecraft.
 4. The panel according to claim 2, wherein the cross-section of the barrier forms an isosceles triangle, the base of which is adjacent to the structure, the angle opposite the base being twice the maximum separation angle.
 5. The panel according to claim 1, wherein: the structure has an elongated shape along a longitudinal axis perpendicular to a transverse axis; and the grid of each cell includes a plurality of conductive wires extending along the longitudinal axis.
 6. The panel according to claim 5, wherein the grid of each cell assumes the form of a comb, the teeth of which are formed by conductive wires extending along the longitudinal axis.
 7. The panel according to claim 5, being on board a spacecraft rotating around an orbit, wherein the longitudinal axis is perpendicular to the plane comprising the orbit.
 8. The panel according to claim 1, wherein the barrier is made from a flexible material, the barrier being suitable for being folded in the space delimited by the two lateral contact faces without protruding relative to the panel surface.
 9. The panel according to claim 1, wherein the barrier is made from a polyimide polymer.
 10. The panel according to claim 1, wherein the barrier is a concentrator.
 11. The panel according to claim 1, wherein the barrier is arranged between each pair of photovoltaic cells between which the voltage is greater than 30V. 